The present invention relates to a control system with a microprocessor, and more particularly to a control system with a microprocessor for preventing a device under control from erroneously operating due to an abnormal operation of the microprocessor.
Recently, a microprocessor has found diverse application in controlling an unlimited number of devices, apparatuses and equipments in a variety of fields. The microprocessor executes control operations of devices under control of a program already designed and prepared. Some disturbances, for example, noise, often puts the microprocessor into an abnormal mode of operation, so that the microprocessor erroneously executes the program. In the approach most often taken for preventing this, the microprocessor is checked as to whether it is in an abnormal mode of operation. When it is determined that the microprocessor is operating abnormally, the microprocessor is immediately reset and returned to a normal mode of operation. However, it may occur that the microprocessor which is operating abnormally is not returned to the normal mode of operation even though it is reset. In such a case, a symptom of the abnormality of the microprocessor operation can be recognized by carefully observing the operation of a device under control by the microprocessor. Therefore, the erroneous control by the microprocessor can be stopped. Some types of such abnormal operations, however, can not be recognized from the operation of a device under control. For example, in the case of controlling a display device, the display device presents the visual contents common to the normal and abnormal operations. It is impossible to check such the abnormal operation and to stop the abnormal running of the microprocessor in such case. This is particularly detrimental to the control of medical equipment such as an endoscope.